The invention relates to a variable valve control for an internal combustion engine having a cylinder head with a valve operating mechanism including a first camshaft with cams for controlling the opening of the engine intake valves and a second camshaft for controlling the closing of the intake valves and a coupler drive disposed between the first and second camshafts for driving the second camshaft with a variable angular position relative to the first camshaft so that the intake valve opening duration can be controlled by controlling the coupler drive.
Variable valve controls of this type are known for example from DE 42 44 550 A1, particularly for the throttle-free load control of gasoline engines by changing the lift and/or opening duration of the intake valves of which each cylinder has at least one. The arrangement of such valve controls includes essentially two camshafts which rotate in opposite directions and which act by way of rocker arms on valves which are spring loaded in a valve closing direction. A first one of the camshafts determines the opening function and the second camshaft controls the closing of the intake valve so that, by changing the angular positions of the camshafts relative to each other, the lift and the opening duration of the valves can be changed in a wide range.
For changing the angular position of the camshafts relative to each other a four gear coupler drive is provided whose input gear is mounted on the first camshaft for rotation with the first crankshaft. The final gear of the coupler drive is mounted on the second camshaft for driving the second camshaft at a variable angular position relative to the first camshaft. The coupler drive includes two intermediate gears which are held in engagement with each other and with the input and the final gears respectively, by coupling arms so that pivoting of the coupling arms about the camshafts forming the pivot axes results in a rotation of the two camshafts relative to each other. The pivoting of the coupling arms is effected in the known designs by a control member which acts on one of the coupling arms and is part of the coupler drive. The control member is supported on the camshaft together with the coupling arm and is actuated by a control motor.
Such a control arrangement is not particularly flexible with respect to the available space, it has a given motion transfer ratio and it is furthermore subjected to the vibrations of the camshaft because it is supported on the camshaft.
It is the object of the present invention to provide a coupler drive arrangement for the camshafts which has good flexibility as to its spatial arrangement and which is not subjected to the vibrations of the camshaft.